The present invention relates to a system and method for emulating an ideal diode for use in a power control device. More specifically, the present invention relates to a system and method for controlling a transistor to emulate an ideal diode.
Conventional diodes are used in any number of applications, and, more specifically, in applications involving rectification. For example, diodes are often used in power conversion systems to convert alternating current into direct current, for over voltage protection, and for blocking reverse currents in systems having multiple power sources (e.g., an uninterruptible power source). The voltage drop across a conventional diode and corresponding power dissipation are generally thought of as being relatively small values. However, power conversion systems typically include high frequency conversion and losses due to diode power dissipation can therefore become substantial. In such case, conventional diodes can be inefficient as compared to diodes having approximately ideal characteristics (e.g., negligible voltage drop).
Theoretical ideal diodes possessing certain preferred characteristics have been proposed. Such theoretical ideal diodes would behave like a short circuit when forward biased and like an open circuit when reverse biased. That is, an ideal diode would dissipate no power in either direction. Empirically no such ideal diode exists, however, approximating such ideal behavior would provide significant benefits related to efficiency and circuit performance.
The actual voltage drop and consequent power dissipation across conventional diodes used in power conversion systems can be substantial under high current conditions. In some cases, the voltage drop across a single diode can be as high as 1.2 volts. In some power conversion applications, the current through a diode can vary from 50 to 400 amps. For a diode with a voltage drop of 1.2 volts carrying 400 amps, 480 watts of power are dissipated. Such large scale power dissipation can adversely affect the reliability of electronics used within or in conjunction with the power conversion system. In some circumstances, for example, such dissipation requires use of a substantial heat sink. Accordingly, the voltage drop across a diode greatly influences efficiency and can require specialized components to dissipate the substantial heat generated.